It is known in the art relating to in-line four cylinder four stroke cycle engines to provide a so-called Lanchester balancer having a pair of balance shafts carried in a housing below the crankshaft and oppositely rotated at twice crankshaft speed to generate a vertical shaking force offsetting the secondary unbalance of the usual four cylinder engine arrangement. One of the shafts is usually driven by a gear or chain from the engine crankshaft and the balance shafts are connected for counterrotation by a pair of drive and timing gears.
A common problem of such balancers is a noise known as gear rattle and generally occurring at engine idle. This rattle is due to the teeth of the timing gears losing contact and impacting the adjacent teeth. It is caused by a fluctuation in crankshaft speed between the firing pulses of succeeding cylinders. Elimination of this gear rattle noise is desired.